kempkes reduction of energy use by efficicent cooling of

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Reduction of energy use by efficient cooling of

strawberries:from model calculation to implementation in a commercial greenhouse

Frank Kempkes, Wageningen UR Greenhouse HorticultureIn cooperation with:Ruud Maaswinkel & Wouter Verkerke: Wageningen UR Greenhouse HorticultureAd van Laarhoven & Marcel Beekers: DLV PlantPeter Geelen: Peter Geelen Horticulture growing analysis and trainingMarcel Dings: Dings aardbeien bv.

Problem of strawberry cultivation: history� Start of crop cycle begin of August

� Enough assimilates (light) for

� Production and flower bud development

But:

� A premature harvest with low production

� Growers postpone start to second half of august.

� Extra energy cost

How to create a cooler night climate?

A grower had already installed coolers in his greenhouse

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Was quite poor:

� It was difficult to reduce greenhouse air temperature during night

How to improve?

� Expert panel with goal:

� Create hypothesis growing strawberries

� How to use and improve efficiency of cooling

� No restrictions to crop production and quality

� Reduction of energy consumption from 20 m3/m2 to 14 m3/m2

Result of cooling

Strawberry expert panel (1)

Series of discussions with a group of experts: strawberry, technicians etc.

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Result of discussion:

Hypothesis: Start in begin of August

� Produces enough assimilates for production and an early start of bud development

� Cooling (reducing night temperature Aug<Sept) will spread production and increase fruit weight

� Synchronize harvest and flower bud development for spring crop cycle results in energy saving

� Create light< and temperature sum nearby “ideal”

According: 13.4 + 0.2 oC per 100 J/cm2


How to reduce energy use?

� Mechanical cooling will increase energy use

� Other cooling methods misting, shading

� In practice severe use of minimum pipe temperatures for humidity control � air movement around the plant

� Misting as cooling method during night?

� Too high humidity

� At high humidity cooling stops

� Natural ventilation (temperature effect) will decrease

� With model calculation optimize the experimental setup

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Model calculations (1)

Course of low cooling result:

heat capacity of the greenhouse (soil)

� Model calculations showed an increase of cooling result when floor was insulated

� Optimization for costs (is insulation rate)

� Permanent? � movable or non movable

� Different effect on greenhouse climate (year around)


Which insulation solutions are feasible? � Sustainable

� Easy to use

� Withstand greenhouse environment

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For climate and energy use movable insulation is best option � solution

Inflatable mattress of aluminized foil

When inflated insulation of warm floor

Cold air flows to fruits


4 8 12 16 2010

15

20

25

30

35[oC]

ref TSoil

ref TFlr

iso TSoil

iso TFlr

Effect insulation

Higher daytime & lower nighttime

� Finally: permanent EPS (extruded polystyrene) plates 40 mm thick

� Energy balance of greenhouse changes

� Effect on soil and floor temperature � air temperature

� Average floor and soil temperature for reference and isolated floor from August 10 – September 10th

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Setup of experiment (3 treatments)

Vertical fans

one per 220 m2

Sect. 2

Night misting with side-wall vents

Sect.1

Reference

Sect .4

Mechanical cooling without floor insulation

Sect. 3

Mechanical cooling with floor insulation

Concrete walk way

Vertical screens for segmentation

Location of side wall fans

Sect. 2

Night misting with side-wall vents

Sect.1

Reference

Sect .4

Mechanical cooling without floor insulation

Sect. 3

Mechanical cooling with floor insulation

Concrete walk way

Vertical screens for segmentation

Location of side wall fansMisting

300 ml/m2/h

Investments

� Local differences

� Shown numbers are a direction for Dutch situation

� Misting 6 € /m2

� Vertical fans 3 € /m2

� Mechanical cooling 20 € /m2

� Side wall fans 2 € /m2

� Insulation 1 € /cm/m2 (4 cm)

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Setup of experiment

Side wall fans capacity 8000 m3/h each

� inside 15 oC, 90%

� outside 20 oC, 50%

Cool capacity rather poor � 30 W/m2

� One unit per 200 m2

� Coolers max capacity 200 W/m2

� With & without distribution ducts

Experiment

Plants (CV Elsanta) were planted August 10 and 11th

Crop cycle divided in three periods:

� August 10 < January 5th and 10th

� 3 – 4 weeks cold

� January 28th – June 13th

� Autumn

� first harvest September 22nd – 28th

� Last harvest December 15th – 22nd

� Spring

� Harvest April 5th – June 13th

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Use of systems: Autumn

misting

Section Cum. Puls time day

[h]

Cum. Puls time night

[h]

coolers

[h]

Side wall fans [h]

1 134 2 134 11 257

3 141 180 4 141 180

� Only 4 % of run time of side wall fans misting could operate� cooling capacity limited

� Extensive use of misting during day time (Aug. – mid. Oct.)

� Coolers only 25 days used

Use of systems: Spring

� Side wall fans & misting not used

� Mechanical coolers not used

� Extensive use of misting during day time (April – June)

� Difference in misting is mainly a side effect of floor insulation

11<01 02<02 24<02 18<03 09<04 01<05 23<05 14<060

50

100

150

200

[date]

[hours]

section 1 & 2

section 3 & 4

No effect expected on climate by experiment except floor insulation}

Cumulated pulse time of misting system in spring

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Experiment: effect of cooling on temperature

16 20 24 4 810

15

20

25

30

35

[hours]

[oC]

sect . 1

sect . 2

sect . 3

sect . 4

out side

Start cooling Stop cooling

� During daytime about 3 oC below outside air temperature

� In night sections 2, 3 and 4 are in average 1.2, 6.7 and 3.7oC lower then section 1 (reference).

August 24th 12:00 till 25th 12:00

Experiment: effect on air temperature

4 8 12 16 2010

15

20

[hours]

[oC]

sect . 1

sect . 2

sect . 3

sect . 4

� Insulation decrease night temperature by 1.5 oC

� Daytime effect in section 3 is result of experimental set<up

� Section 3 more humid (RH)

Average twenty<four hours temperature course August – December

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Experiment: effect on air temperature

33 38 43 48 5310

12

14

16

18

20

daytemp. [oC]

weeknumber

sect. 1

sect. 2

sect. 3

sect. 4

ideal

� Week 33 – 40 section 3 about as ideal

� Week 40 – 53 section 1 about ideal rest to cold

Average week temperature

Experiment: effect on humidity

4 8 12 16 2075

80

85

90

95

[hours]

RH [%]

sect. 1

sect. 2

sect. 3

sect. 4

� During night because of low temperatures higher humidity

Average RH during day between August 11th and January 5th

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Experiment: energy use autumn

11<8 1<9 22<9 13<10 3<11 24<11 15<12 05<010

50

100

150

200

250

[MJ/m

2]

sect. 1

sect. 2

sect. 3

sect. 4

� Differences between section 1 & 4 and 2 & 3 are small

� Continuation of heating in section 3 and 4 for 6 days cost about 25 MJ/m2

Cumulated energy use in autumn

1m3 natural gas is 31.65 MJ

Experiment: effect on climate & energy

section Degrees hours [oC] Energy use [MJ/m2]

cooling heating 08/10 –

09/11 Autumn Spring Autmn Spring total Autumn Spring total

1 11534 38381 36138 184 210 394 2 11342 37433 34238 218 220 438 3 10224 35328 34332 34 – 34 240 220 460 4 11082 37185 35581 43 – 43 197 216 413

� Autumn section 3 lowest in degrees hours

� Spring section 2 and 3 lowest but differences smaller

� In spring as expected small differences in energy use

� Overall energy use section 3 highest

� Difference in cooling energy is air temperature difference

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Results: Crop

section Production [kg/m2]

Aut-

umn spring total

1 5.2 9.3 14.5 2 5.4 9.6 15.0 3 5.4 9.2 14.6 4 5.4 9.6 14.9

� Over whole crop cycle (Aug – May) no significant differences in

� Crop growth

� Yield

� Quality

� Average fruit weight.

Results: Crop

� During active cooling in cooled sections

� Plant load lower

� Average fruit weight higher

� Production of fruits lower

� Cooling was realized according to plan but we did not not succeeded to spread the harvest.

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Conclusions (1)

� Mechanical cooling in combination with floor insulation can reduce night temperature.

� Mechanical cooling increases energy use

� Where is the cold water produced? � not taken into account in shown numbers

� Planting date in sections with mechanical cooling was about a week to late.

Conclusions (2)

� Misting has more effect on climate then mechanical cooling.

� Reduces even at day time greenhouse air temperature

� It will increase humidity (prevents extreme low humidity with young plants)

� Use of cooling systems was limited (in time)

� Expensive investment

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Conclusions (3)

� Energy use by early start in august in combination with use of vertical fans drops from around 20 m3/m2

(common practice) to about 14 (season 2009<2010)

� Main energy saving is result of reduction of use of minimum pipe

� On time start 2 < 2 .5 m3/m2

� Small increase of energy use by floor insulation

Questions?

kempkes reduction of energy use by efficicent cooling of

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